| 1. |
- Abdolmaleki, Mehdi, et al.
(författare)
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Exploration of IOCG Mineralizations Using Integration of Space-Borne Remote Sensing Data with Airborne Geophysical Data
- 2020
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Ingår i: XXIV ISPRS Congress, Commission III (Volume XLIII-B3-2020). - : International Society of Photogrammetry and Remote Sensing (ISPRS). ; , s. 9-16
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Konferensbidrag (refereegranskat)abstract
- Nowadays, remote sensing technologies are playing a significant role in mineral potential mapping. To optimize the exploration approach along with a cost-effective way, narrow down the target areas for a more detailed study for mineral exploration using suitable data selection and accurate data processing approaches are crucial. To establish optimum procedures by integrating space-borne remote sensing data with other earth sciences data (e.g., airborne magnetic and electromagnetic) for exploration of Iron Oxide Copper Gold (IOCG) mineralization is the objective of this study. Further, the project focus is to test the effectiveness of Copernicus Sentinel-2 data in mineral potential mapping from the high Arctic region. Thus, Inglefield Land from northwest Greenland has been chosen as a study area to evaluate the developed approach. The altered minerals, including irons and clays, were mapped utilizing Sentinel-2 data through band ratio and principal component analysis (PCA) methods. Lineaments of the study area were extracted from Sentinel-2 data using directional filters. Self-Organizing Maps (SOM) and Support Vector Machines (SVM) were used for classification and analysing the available data. Further, various thematic maps (e.g., geological, geophysical, geochemical) were prepared from the study area. Finally, a mineral prospectively map was generated by integrating the above mentioned information using the Fuzzy Analytic Hierarchy Process (FAHP). The prepared potential map for IOCG mineralization using the above approach of Inglefield Land shows a good agreement with the previous geological field studies.
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| 2. |
- Alakangas, Lena, et al.
(författare)
-
Min-North : Development, Evaluation and Optimization of Measures to Reduce the Environmental Impact of Mining Activities in Northern Regions
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Min-North (Development, Evaluation and Optimization of Measures to Reduce the Environment Impact of Mining Activities in Northern Regions) project was a trans-national cooperative project, with participants from the Geological Survey of Finland (GTK), University of Oulu (UO), UiT The Arctic University of Norway (UiT), Luleå University of Technology (LTU) and SMEs from Sweden, Finland and Norway. The project was funded by Interreg Nord and Norrbottens länsstyrelse. The participants have expertise in mine waste management, mine water treatment and geophysics. The overall aim of the project was to enhance the development of environmental protection technologies. An associated goal was to deepen cross-border cooperation by creating a larger critical mass of researchers in mine waste management and local SMEs in the Northern regions with greater capacities to disseminate and implement new methods, products and services. The project ran for 36 months from the 1st of January 2016 to the end of December 2018.
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| 3. |
- Appel, Peter W.Uitterdijk, et al.
(författare)
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Unusual features caused by lightning impact in West Greenland
- 2006
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Ingår i: Geological Magazine. - : Cambridge University Press. - 0016-7568 .- 1469-5081. ; 143:5, s. 737-741
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Tidskriftsartikel (refereegranskat)abstract
- Two lightning impacts are described from an area near the Inland Ice in West Greenland. The first lightning blasted an outcrop of metacherts. It subsequently split into two branches, which traversed rock outcrops and boulders, leaving behind two white almost straight lines, 30 m and 14 m long, respectively, where all lichens and plants were burned away. On the white lines the upper few millimetres of the traversed boulders were melted to a glass which subsequently peeled off by thermal expansion to leave a rough surface. Magnetic investigation of an amphibolite boulder found on the white line showed that a strong electric current indeed traversed the boulder. A few years later a second lightning impacted on a mountaintop close to the first impact. The second lightning left a trail on the rock surface covered by a thin layer of glass. The glass displays spectacular colours ranging from metallic blue to red, yellow and green.
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| 4. |
- Ask, Maria, et al.
(författare)
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The Innovative Exploration Drilling and Data Acquisition Research School
- 2021
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Ingår i: NSG2021 27th European Meeting of Environmental and Engineering Geophysics. - : European Association of Geoscientists and Engineers.
-
Konferensbidrag (refereegranskat)abstract
- The Innovative Exploration Drilling and Data Acquisition Research School (I-EDDA-RS) is aimed at educating emerging scientists and engineers in on-site drilling and geoscientific investigation technology for mining. I-EDDA-RS consists if a consortium of scientists and specialists from six universities and research institutes in Germany and Sweden. A central component of the research school is that the courses have hands-on components at drill sites, boreholes and repositories. In addition, a course on entrepreneurial skills required in the exploration industry is also included in I-EDDA-RS. The arrival of the Covid-19 pandemic resulted in altered plans. Instead of offering ten courses with strong field work, practical, and entrepreneurial components during 2020, four courses via distant learning were offered. While this was disappointing in many aspects, two of the courses attracted a larger group of students from a wider part of the world than original envisioned. Outreach via on-line and open webinars is also a route to explore, as a complement to meetings and conferences in real life. The I-EDDA-RS courses in 2021 welcomes students at MSc & PhD level, as well as experienced professionals for lifelong learning (c.f. https://www.iedda.eu/rs). The form and type of teaching is to be determined.
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| 5. |
- Basokur, Ahmet Tuǧrul, et al.
(författare)
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Comparison of induced polarization and controlled-source audio-magnetotellurics methods for massive chalcopyrite exploration in a volcanic area
- 1997
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Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 62:4, s. 1087-1096
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we compare and contrast the results of field experiments with the dipole-dipole-induced polarization (IP) and controlled-source audio-magnetotellurics (CSAMT) methods, along the same survey profiles, at a test area that was subject to extensive drilling and detailed geological investigation. The ore bodies are interbedded between two series of dacitic tuff. The depth and thickness of the massive chalcopyrite-pyritesphalerite body vary between 25 and 100 m and 0.5 and 16 m, respectively. Resistivity and IP phase measurements on the core samples collected from the test area provide some idea of the relative differences between the background rock units and the target. The resistivity of the chalcopyrite samples varies between 0.6 to 2 ohm-m and provides sufficient resistivity contrast with surrounding volcanic rock units for target detection. The results of dipole-dipole IP profiling with a 50-m dipole length conducted along two profiles are presented in the form of apparent resistivity and phase pseudosections. CSAMT measurements were made at 13 frequencies from 2 Hz to 8192 Hz along three profiles. The receiver dipole length was 25 m. The CSAMT data are presented in the form of pseudosections using conventional and new definitions of apparent resistivity. The elliptical contours of low apparent resistivity generated by the transition-field notch can be misleading with respect to the real anomaly of the ore body. These artificial anomaly patterns are suppressed by making use of an alternative apparent resistivity definition derived from the frequency-normalized impedance. The qualitative interpretation based on the IP and CSAMT pseudosections shows that the location and the extension of the ore body are indicated better in the CSAMT apparent resistivity data computed from the alternative definition. The qualitative interpretation of the IP data is difficult because of the 3-D effect arising from the neighboring thicker parts of the ore body and pyrite particles within the basement. At the final stage, the far-field range of the CSAMT apparent resistivity and phase data is identified by the visual inspection of the individual sounding diagrams. The models derived from the 2-D Occam inversion carried out on the far-field data are compared with the drill-hole information and are found to describe the actual geological situation.
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| 6. |
- Bedini, Enton, et al.
(författare)
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Use of airborne hyperspectral and gamma-ray spectroscopy data for mineral exploration at the Sarfartoq carbonatite complex, southern West Greenland
- 2018
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Ingår i: Geosciences Journal. - : Springer. - 1226-4806 .- 1598-7477. ; 22:4, s. 641-651
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Tidskriftsartikel (refereegranskat)abstract
- The Sarfartoq carbonatite complex occurs in the transition zone between Archaean and Paleoproterozoic gneisses in southern West Greenland. The Sarfartoq carbonatite complex hosts ore deposits and occurrences of rare earth elements and niobium. In this study, airborne HyMap hyperspectral imagery and coincident airborne gamma-ray spectroscopy data were analysed for mineral exploration of Sarfartoq carbonatite complex. The study area included the carbonatite core zone and a hydrothermally altered shear zone prospective for rare earth elements mineralization in the southern margin of the carbonatite complex. The analysis of the hyperspectral imagery was focused on the mapping of the spatial distribution of carbonatite, fenite and limonite. Significant anomalies of uranium, thorium and potassium were outlined from the gamma-ray spectroscopy data. Decision trees were used to combine the results from the hyperspectral image analysis and airborne gamma-ray spectroscopy. Significant anomalies of thorium at the hydrothermally altered shear zone coinciding with the presence of carbonatite rocks are generally indicative of outcropping rare earth element mineralization. The study indicates the benefits of coincident airborne hyperspectral and gamma-ray spectroscopy surveys for the mineral exploration of carbonatite complexes.
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| 7. |
- Belay, R., et al.
(författare)
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One‐dimensional non‐linear inversion of magnetotelluric data : the importance of data errorrs
- 1995
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Ingår i: Geophysical Prospecting. - : Wiley-Blackwell. - 0016-8025 .- 1365-2478. ; 43:7, s. 905-918
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Tidskriftsartikel (refereegranskat)abstract
- Inversion of noisy magnetotelluric data over a horizontally stratified earth has no unique solution. Instead, the resistivities and thicknesses of the layers can only be specified to lie within certain bounds at a particular confidence level. The significance of having correctly estimated data errors when calculating the parameters and parameter bounds is discussed. Emphasis is put on the very corrunon problem of not being able to obtain models which can be considered acceptable with a reasonable certainty from a statistical point of view. A method is presented to obtain a pragmatic data error description by adjustment of wrongly estimated data errors while keeping the suppression of 1D data features at a minimum. A comparison is made between calculation of the parameter bounds based on approximating the confidence surface by hyperellipsoids and a calculation based on a full non‐linear most‐squares analysis. In general it is found that the approximation works very well when the confidence limit is small. However, significant deviations are found in some cases.
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| 8. |
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| 9. |
- Brethes, Anaïs, et al.
(författare)
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3D-Modelling of the Early Triassic Base-Metal Mineralized Syn-Rift Sequence in the Jameson Land Basin (East Greenland)
- 2015
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Ingår i: Mineral Resources in a Sustainable World. - 9782855550664 ; , s. 1701-1704
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Konferensbidrag (refereegranskat)abstract
- The Jameson Land Basin in central East Greenland is mineralized in Pb, Zn and Cu. Mineralization occurs in several stratigraphic horizons and along structures in Upper Permian and Triassic sediments. A good understanding of the basin architecture and evolution is therefore essential for mineral exploration in this area. 3D-Photomapping from high resolution aerial photos along with a structural interpretation of aeromagnetic data, electromagnetic data, and results from fieldwork and drilling were integrated into a 3D-structural model. This data integration allowed modelling the rift architecture in the eastern margin of the Jameson Land Basin.
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| 10. |
- Brethes, Anaïs
(författare)
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An integrated study of geological, magnetic and electromagnetic data for mineral exploration in the Jameson Land Basin, central East Greenland
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Jameson Land Basin, located in central East Greenland, initiated in Devonian time with the collapse of the over-thickened Caledonian Orogen. The basin developed during different phases of rifting from the late Paleozoic to the Mesozoic and has accumulated between 16-18 km of sediments. In Paleogene time, the basin was affected by intense magmatism due to the opening of the North Atlantic Ocean c. 55 Ma ago. Due to a significant uplift in Miocene time, the sedimentary sequence is well exposed along the basin margins, revealing numerous mineral occurrences hosted within almost the entire stratigraphic succession. The major types of mineralization comprise: (1) intrusion-related Mo (± Pb, Zn, Cu, Ag) mineralization associated with Paleogene intrusive complexes; (2) stratabound and/or stratiform Cu, Pb, Zn, (Ag) within Upper Permian and Triassic clastic and marine sedimentary formations; (3) stratabound and structurally controlled Pb-Zn, Cu, Ba, (Sr) mineralization in Upper Permian carbonates; and (4) structurally-controlled Pb, Zn, Cu (±Sb, Bi, Ag, Au) vein-type mineralization within Caledonian and Paleozoic rocks.It is well acknowledged that structures such as faults, thrusts, detachments, shear zones and associated fracture systems play an important role as fluid conduits connecting metal sources and sites of mineral precipitation. In particular, previous studies showed that mineral occurrences within the East Greenland Caledonides are closely related to lineaments and intrusions. In this context, the Crusmid-3D project was initiated in 2014, aiming at establishing the links between the crustal structures and the mineral occurrences in the Jameson Land Basin using a combination of geological and geophysical data. The interest for mineral exploration in the area led exploration companies and institutions to carry out magnetic and electromagnetic surveys, and the data derived from these constitute the base of this study.This thesis provides a detailed structural interpretation of aeromagnetic data in the Jameson Land Basin where several magnetic trends associated with Tertiary dikes and sills as well as with reactivated Paleozoic and Triassic faults were delineated. These data, in combination with a literature review and compilation of the mineral occurrences in the Jameson Land Basin, allowed highlighting seven prospective areas for structurally-controlled base metal mineralization.New structural data from geological fieldwork, drilling results and geophysical data (magnetic, electromagnetic and seismic data) along the eastern margin of the basin allowed a new interpretation of the geometry of the Triassic rift in East Greenland, represented by NE-SW-trending basins and highs segmented by NW-SE-trending transfer zones. It can be correlated with its European conjugate margin, displaying analogies with the Triassic Froan and Helgeland Basins in the Norwegian offshore and with the Papa and West Shetlands Basins north of the Shetland Islands.The proposed structural model of the Triassic rift was further investigated using 3D-geologically-constrained inversion of magnetic data in order to refine the architecture of the eastern margin of the Jameson Land Basin. Modelling results confirmed the presence of a shallow westward dipping peneplained crystalline basement in the southern part of the area while the northern part is characterized by faulted blocks, which accommodated relatively thick red bed sedimentary sequences, thereby representing a good potential source of base metals.Furthermore, Induced Polarization (IP) effects observed in airborne time-domain electromagnetic data acquired in the eastern margin of the basin were investigated using Self-Organizing Maps (SOM). The analysis of the shape and amplitude of the transient response curves using the SOM allowed identifying four areas where the transient curve patterns exhibit strong IP effects. These are shown to be collocated with Tertiary sills and dikes, clay-altered rocks as well as with a sulfide-bearing brecciated granite and with Triassic stratigraphic horizons hosting disseminated base metal sulfides.
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| 11. |
- Brethes, Anaïs, et al.
(författare)
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Geological Analysis of Aeromagnetic Data over the Blyklippen Lead-zinc Mine at Mesters Vig, Central East Greenland
- 2016
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Ingår i: First Conference on Geophysics for Mineral Exploration and Mining. - Netherlands : European Association of Geoscientists and Engineers. - 9789462821958
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Konferensbidrag (refereegranskat)abstract
- In the Mesters Vig area epithermal Pb-Zn sulphide-bearing quartz veins are associated with the border faults of a NNW-SSE elongated graben down-faulting Carboniferous to Lower Triassic sediments. The analysis of the total magnetic field, tilt derivative, vertical derivative and analytic signal allowed to define subcropping magnetic domains and identify structural trends. Doleritic dykes, sills and faults were mapped and structural relationships were established between them. Finally, aeromagnetic data allowed here to delineate structural trends along and in the vicinity of which mineralized quartz veins are mapped.
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| 12. |
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| 13. |
- Brethes, Anais, et al.
(författare)
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Interpretation of aeromagnetic data in the Jameson Land Basin, central East Greenland : Structures and related mineralized systems
- 2018
-
Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 724-725, s. 116-136
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a detailed interpretation of several aeromagnetic datasets over the Jameson Land Basin in central East Greenland. The interpretation is based on texture and lineament analysis of magnetic data and derivatives of these, in combination with geological field observations. Numerous faults and Cenozoic intrusions were identified and a chronological interpretation of the events responsible for the magnetic features is proposed built on crosscutting relationships and correlated with absolute ages. Lineaments identified in enhanced magnetic data are compared with structures controlling the mineralized systems occurring in the area and form the basis for the interpretations presented in this paper. Several structures associated with base metal mineralization systems that were known at a local scale are here delineated at a larger scale; allowing the identification of areas displaying favorable geological settings for mineralization. This study demonstrates the usefulness of high-resolution airborne magnetic data for detailed structural interpretation and mineral exploration in geological contexts such as the Jameson Land Basin.
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| 14. |
- Brethes, Anaïs, et al.
(författare)
-
Mapping and characterization of Induced Polarization in airborne TEM data from central East Greenland : application of a Self-Organizing Map procedure
- 2016
-
Konferensbidrag (refereegranskat)abstract
- nduced Polarization (IP) effects were observed in airborne Time Domain EM (TEM) data acquired in central East Greenland in the context of exploration for disseminated sulphides in a sedimentary basin. Some of the IP anomalies were targeted by drilling which revealed the absence of mineralization. In order to understand the possible causes of the IP effects we first identified them in the TEM data. IP indicators were extracted from the shape of the transient curves at every measurement location and were analysed by using a Self-Organizing Map (SOM) procedure. Results from K-mean clustering of the SOM are visualized on a geographical map showing the transient curves’ characteristics. Some of the clusters are clearly correlated with the geology whereas others merely reflect recordings below the noise level. In order to interpret the cause of the IP anomalies the airborne TEM data were inverted for the Cole-Cole parameters.
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| 15. |
- Chouliaras, Gerassimos, et al.
(författare)
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The application of the magnetotelluric impedance tensor to earthquake prediction research in Greece
- 1988
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 152:1-2, s. 119-135
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Tidskriftsartikel (refereegranskat)abstract
- Continuous short period (0.1-3600 s) measurements of the magnetotelluric field components were conducted simultaneously at two sites in Greece for a period of 5 weeks. The estimation of the impedance tensor elements from 8-hr windows of recorded data, at each station, is found to describe the local electromagnetic induction with great accuracy. The computation of the residual electric field, obtained as the difference between the observed and estimated inductive part of the electric fields, clearly improves the detection of any local electric field anomaly. This method was used in an attempt to detect precursory Sci smic electrical signals (SES) that have been reported to precede earthquakes in Greece. The results indicate the success of this method in resolving ambiguities about the nature of the reported SES, i.e. whether it has an external or internal source. Although during the recording period no large earthquake occurred, five with a magnitude of between ML = 4.0 and ML = 4.3 occurred within a radius of 150 km from one of the stations. The magnetotelluric recordings and the computed residual electric fields for the time intervals reported to contain the SES precursors to these events were analysed in some detail. In two of the cases it was found that the sources could not be related to earthquake processes. In the other three cases the nature of the source of the suspected SES, although electric, could not be established with certainty. These results indicate that for earthquakes of small magnitude (ML ≤ 4.3) or of large epicentral distance (r ≥ 100 km), the detection of a SES is extremely difficult.
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| 16. |
- Darwesh, Ali, et al.
(författare)
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Evaluation of Limestone Interval in the Drilled Surface Section of Bn-1 Oil Well
- 2016
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Ingår i: Engineering. - : Scientific Research Publishing, Inc.. - 1947-3931 .- 1947-394X. ; 8:8, s. 515-524
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Tidskriftsartikel (refereegranskat)abstract
- The first exploration oil well in any oil block consumes in general more time and cost than the other wells in the same block. Evaluating the drilled wells serves to improve the future operations. This paper evaluates the drilled surface section through real field data for the first exploration oil well drilled in one of the oil blocks, in Kurdistan north of Iraq. The surface section of the well was drilled with the conventional method to penetrate many different geological formations with tight intervals. Drilling efficiency and the difficulties encountered are discussed and explained using various data sources. All daily drilling reports concerning a specific interval were studied. This includes weight on bit, string rotation, mud pump flow and penetration rate. Evaluation was carried out by analyzing the used controllable drilling parameters with the formations features. Penetration of the Pila Spi formation (Middle Eocene) was the most difficult formation in the drilled section. Microsoft Office 365 Pro Plus used in making graphs and Excel tables. Evaluations showed that the conventional technology used left many negative effects, like increase in None Productive Time NPT, cost and ground water pollution. Simultaneous Casing Drilling method proposed as an alternative method for the future campaign.
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| 17. |
- Darwesh, Ali K., et al.
(författare)
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Kicks controlling techniques efficiency in term of time
- 2017
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Ingår i: Engineering. - : Scientific Research Publishing. - 1947-3931 .- 1947-394X. ; 9:5, s. 482-492
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Tidskriftsartikel (refereegranskat)abstract
- Kicks are the result of under balance drilling operation. Time consumed to control the kicks will be different in depending on the controlling technique. Drilling fluid considered as a first barrier to control formation pressure and well kicks. Any advance in drilling fluids leads to more controlled operation in term of time. This paper will follow the general increasing profile of pressure before entering the reservoir. Both methods of well controlling technique; circulating techniques and non-circulating have been implemented in many oil blocks. The process of designing and casing selection, setting depth and many other issues is predominately dependent on the utilization of accurate values of formation pressure. Formation pressures used to design safe mud weights to overcome fracturing the formation and prevent well kicks. Hence the emphasis has been placed on the practical utilization of kicks pressure near the reservoir. The presented relationships will help the engineer to better understand lithological columns and reduce potential hole problems during the kick appearance. Selecting the best well controlling practical method can lead to not harming the reservoir and more production later. Changes in some drilling fluid properties have been proposed with increasing the depth without damaging the reservoir. Suggestions in relation to the casing setting point of the intermediate section are also proposed. Standard equations with proper modification for gases and safety margin have been proposed for the future drilling operation in oil fields above the reservoir.
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| 18. |
- Darwesh, Ali K., et al.
(författare)
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Time Optimizing near the Pay Zone
- 2017
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Ingår i: Engineering. - : Scientific Research Publishing. - 1947-3931 .- 1947-394X. ; 9:10, s. 848-858
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Tidskriftsartikel (refereegranskat)abstract
- Well control techniques are used in oil and gas drilling operations to control bottom hole pressure and avoid any fluid influx from formation to the well. These techniques are highly important near the pay zone in term of time. Controlling formation fluid pressure and thereby the formations behavior in a predictable fashion will help toward more optimized environmental friendly drilling operation. Time consumed to control the formation fluid pressure will range between few hours to many days. This paper discusses hydrostatic pressure distribution and changes near the pay zone for one oil blocks in Kur- distan, in the northern part of Iraq. Obtaining homogeneous increase in some drilling fluid properties will help the engineer to better interpret sampling of the lithological columns and reduce potential hole problems and operationtime.
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| 19. |
- Darwesh, Ali, 1966-
(författare)
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Parameters optimization of oil well drilling operation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the beginning of 2005, the ministry of natural resources in the Kurdistan region of Iraq dividedits territory into more than 50 oil blocks based on geological setting. These oil blocks were awardedlater to different international oil companies for oil investments based on Production SharingContracts (PSCs). A new oil-exporting pipe was also established from the region to the Jaihan portin Turkey at the Mediterranean Sea.This study is related to the oil well drilling operations in one of these oil blocks in northern Iraqwhich is referred as the Bazian oil block. Drilling operations in the nearby oil blocks (Taq Taq andMiran) were started earlier and the drilling data of those oil blocks were used as offset data in thedrilling program of the Bazian block. High similarities were expected between these oil blocks withrespect to lithology of the formations, oil well drilling techniques, and operation problems. By 2009over twenty oil wells were drilled in the Taq Taq oil block and it is becoming one of the mostimportant oil fields in the Kurdistan region. In the Miran oil block, exploration for oil and gas startedin early 2008, and three oil wells were completed and started to produce crude oil. By the end of2009, the geological and geophysical surveys in Bazian block were finished and the drilling operationstarted on October 1st the same year.This study (Parameter Optimization in Oil Well Drilling Operation) was recommended andsponsored by the Kurdistan Regional Governorate (KRG) aiming towards more optimized drillingin the future in the same oil block. Parameters like weight on bit, string rotation and rate ofpenetration for the future drilling operation in the Bazian oil block with more optimized valueswere predicted. This study was started by collecting detailed operational data from different sourcesduring the operations of drilling the Bazian well Bn-1. Among many sources of data, Mud LoggingUnit (MLU) data were selected for this study, as it was the most complete data set from the surfaceto the final drilled depth. This thesis contains the work of five published papers in the evaluation ofthe drilling operation at different intervals for the key well. Parameters for achieving the optimalpenetration rate were predicted for the future operations.The first paper (Evaluation of Limestone Interval in the Drilled Surface Section of Bn-1 Oil Well)was on the evaluation of the drilling operation in the surface section from 9 m to 480 m. The highlyfractured Pila Spi formation was studied for its controllable parameters like Weight on Bit (WOB),drill string rotation (RPM) and the used torque. High loss of circulation and environmental effectswere studied. Optimum drilling fluid, drilling technique, and drilling parameters were proposed forthe future drilling operation.In the second paper (Kicks Controlling Techniques Efficiency in Term of Time) recorded data wereanalyzed to manage the drilling operation during the critical times in terms of controlling the BottomHole Pressure (BHP). Productive and none productive times were analyzed through the study ofthe drilling and tripping operations. Change in the drilling technique was proposed by modifyingthe drilling fluid. Drilling fluid as a first barrier to control formation pressure and well kicks werestudied for their rheological properties. During the drilling operations two techniques, circulatingtechniques and non-circulating methods, were implemented to control the BHP. Both methodshave been implemented to control kicks in the Bn-1 oil well and wells in other oil blocks in theregion. The process of drilling design and casing setting points have been studied based on theutilization of accurate values of formation pressure. Data of formation pressures were used to designsafe mud weights to overcome and prevent well kicks. The emphasis has been placed on the practicalutilization of the kicks pressure near the reservoir. The presented relationships help in betterunderstanding of the lithological columns and reduce possible hole problems during the kickappearance. Optimum casing setting point of the intermediate section was proposed for futureoperations.The third paper (Time Optimizing near the Pay Zone) was on the drilling operation inside the caprock. Time managing was studied for surface preparation facilities, subsurface expected pressurecontrol time, and the best technique to control the Bottom Hole Pressure (BHP). Well controllingtechniques in oil and gas drilling operations are used to control BHP and avoid any fluid influx fromformation to the well. Time consumed to control the formation pressure will range between a fewhours to many days. This paper also discussed the hydrostatic pressure distribution and changes nearthe pay zone for the Bazian (Bn-1) oil well. Increasing linearly drilling fluid properties such as densityand viscosity with time will help the engineer to better interpret sampling of the lithological columnsand reduce possible hole problems.Paper number four (Wiper Trips Effect on Wellbore Instability Using Net Rising Velocity Methods)was on the effect of wiper trips operations to control parameters during the operations in two drilledshale formations, the Tanjero and Shiranish formations. Wiper trips were evaluated based on thelifting capacity of the cutting in the drilling fluid. This paper discussed the wiper trip effects on wellinstability in shale formations. The problematic shale interval sections were studied with respect tothe time spent on the wiper trip operations. Lifting efficiency and well wall instability arecontinuously changing with time. Detailed drilling operation, formation heterogeneity, rheologicaland filtration characteristics of the proposed polymer water-based mud were discussed. The physicaland chemical properties of the drilled formation and drilling fluid were also studied.Wiper trips were analyzed based on recorded history in relationship with the controllable parameters.Two calculation models have been implemented to find the net rising cutting particle velocity inthe annular. The relation between the net rising velocity and wiper trips were analyzed with supportof results from laboratory works. Strong relationships were found between the wiper trip effects andlithology types of the penetrated shale. A modified drilling program was proposed in relationship tothe casing setting point and drilling fluid properties that make the operations more optimized.The fifth paper (Controllable drilling parameter optimization for roller cone and polycrystallinediamond bits) predicts optimized Rate of Penetration (ROP), WOB and the string rotation (RPM– rotation per minute) for the entire drilled well. The most used empirical Bourgoyne and Youngmodel (BYM) for roller cone bits were used in the optimization process. This model describes theeffect of eight parameters in one mathematical equation. The BYM was adjusted to be applicablefor other types of drilling bits like polycrystalline diamond compacts (PDC) bits. Controllableparameters like WOB, RPM and ROP were clustered based on changes in Bottom Hole Assembly(BHA) and lithology before running the model.The implemented clustering and averaging method for the collected data in short lithologicalintervals were used to eliminate the effect of noisy data and to overcome the lithology homogeneityassumption used in other previous studies. A simpler model were introduced instead to optimize thestring rotation.Multiple regression techniques were used in each cluster to determine optimized controllable drillingparameters. Optimized ROP, WOB, and RPM were predicted for future drilling operations. Aclear relationship was found between the formation lithology and the controllable parameters ineach cluster.
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| 20. |
- Darwesh, Ali, et al.
(författare)
-
Wiper Trips Effect on Wellbore Instability Using Net Rising Velocity Methods
- 2018
-
Ingår i: Open Petroleum Engineering Journal. - Sharja, UAE : Bentham Science Publishers. - 1874-8341. ; 11, s. 14-28
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Tidskriftsartikel (refereegranskat)abstract
- Background: This paper discusses the wiper trip effects on well instability in shale formations.Objectives: Problematic shale interval sections have been studied for the time spent on the wiper trip operations. Lifting efficiency and well wall instability change with the time analyzed. Detailed drilling operation, formation heterogeneity, rheological and filtration characteristics of polymer water-based mud are discussed. Physical and chemical properties of the drilled formation and drilling fluid are also studied.Materials and Methods: Wiper trips are analyzed using a typical drawing program to find the relations between the most controllable parameters. For that, two calculation models have been implemented to find the net rising cutting particles velocity in the annular. The relation between the net rising velocity and wiper trips is analyzed. Laboratory works have been done to support the findings of field work.Results: Strong relations have been found between the wiper trip impacts and lithology types of the penetrated shale.Conclusion: A modified drilling program is proposed in relation to changes in casing setting depth and drilling fluid properties that make the operations more efficient in cost and time.
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| 21. |
- Døssing, Arne, et al.
(författare)
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A High-Speed, Light-Weight Scalar Magnetometer Bird for km Scale UAV Magnetic Surveying : On Sensor Choice, Bird Design, and Quality of Output Data
- 2021
-
Ingår i: Remote Sensing. - : MDPI. - 2072-4292. ; 13:4
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic surveying is a widely used and cost-efficient remote sensing method for the detection of subsurface structures at all scales. Traditionally, magnetic surveying has been conducted as ground or airborne surveys, which are cheap and provide large-scale consistent data coverage, respectively. However, ground surveys are often incomplete and slow, whereas airborne surveys suffer from being inflexible, expensive and characterized by a reduced signal-to-noise ratio, due to increased sensor-to-source distance. With the rise of reliable and affordable survey-grade Unmanned Aerial Vehicles (UAVs), and the developments of light-weight magnetometers, the shortcomings of traditional magnetic surveying systems may be bypassed by a carefully designed UAV-borne magnetometer system. Here, we present a study on the development and testing of a light-weight scalar field UAV-integrated magnetometer bird system (the CMAGTRES-S100). The idea behind the CMAGTRES-S100 is the need for a high-speed and flexible system that is easily transported in the field without a car, deployable in most terrain and weather conditions, and provides high-quality scalar data in an operationally efficient manner and at ranges comparable to sub-regional scale helicopter-borne magnetic surveys. We discuss various steps in the development, including (i) choice of sensor based on sensor specifications and sensor stability tests, (ii) design considerations of the bird, (iii) operational efficiency and flexibility and (iv) output data quality. The current CMAGTRES-S100 system weighs ∼5.9 kg (including the UAV) and has an optimal surveying speed of 50 km/h. The system was tested along a complex coastal setting in Brittany, France, targeting mafic dykes and fault contacts with magnetite infill and magnetite nuggets (skarns). A 2.0 × 0.3 km area was mapped with a 10 m line-spacing by four sub-surveys (due to regulatory restrictions). The sub-surveys were completed in 3.5 h, including >2 h for remobilisation and the safety clearance of the area. A noise-level of ±0.02 nT was obtained and several of the key geological structures were mapped by the system.
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| 22. |
- Døssing, A., et al.
(författare)
-
A Multidisciplinary UAV- and Ground-Geophysical Mapping of Complex Mineralisations in an Inter-Tidal Coastal Zone, Brittany (France)
- 2020
-
Ingår i: NSG2020 3rd Conference on Geophysics for Mineral Exploration and Mining. - : European Association of Geoscientists and Engineers.
-
Konferensbidrag (refereegranskat)abstract
- Getting reliable geophysical and geological 3D models of the subsurface is an absolute necessity for successful resources exploration. Here, we show how novel UAV-borne geophysical mapping can be extremely valuable for mapping potential new exploration areas that are difficult to access by foot, such as hard rock inter-tidal zones and boulder beaches. We show the results from a multidisciplinary geophysical campaign of highly magnetic dikes and granites along a boulder beach in Brittany, France. Our mapping is carried out using customized geophysical sensor systems with high quality sensors. These include in particular a special designed UAV-towed magnetometer bird and multispectral system for large area mapping purposes. The UAV-borne mapping is supplemented by ground-based gamma-ray spectrometry data and ground-based magnetic gradiomety data. The results clearly demonstrate the value of UAV-borne systems in difficult areas as compared to traditional mapping methods as well as the value of combining various geophysical sensors for exploring the economic geology. All UAV-borne data were collected during two days, while the ground-based data – covering only the inner and dry part of the beach - were collected over seven days.
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| 23. |
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| 24. |
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| 25. |
- Elming, Sten-åke, et al.
(författare)
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Results of magnetotelluric and gravimetric measurements in western Nicaragua, central America
- 1997
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 128:3, s. 647-658
-
Tidskriftsartikel (refereegranskat)abstract
- Studies a ca. 170 km long traverse running from the Pacific coast of Nicaragua in the west to the Nicaraguan Highland in the east. This part of Nicaragua is characterized by sedimentary rocks of the Pacific Coastal Plain, separated from the Tertiary volcanic rocks of the Highland by the NW-SE-trending Nicaraguan Depression. The purpose of this study is to provide electric conductivity and density constraints on geological crustal structures along the transect. This may then serve as a base for the understanding of the tectonic evolution of this part of Central America. Questions to be answered are: (1) is the Pacific coastal province an accreted terrane? (2) What is the character of the depression? Is this a hidden contact between an accreted terrane and the continental Chortis block? (3) If so, is there a different physical signature for the crust of the Pacific province compared to that of the Highlands?
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| 26. |
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| 27. |
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| 28. |
- Gao, Jingyu, 1992-
(författare)
-
Three-Dimensional Modelling and Inversion of DC resistivity and Time Domain EM data using Multi-Resolution Framework
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 3-D forward modelling and inversion techniques play an important role in data interpretation, but they are still computationally challenging tasks. Therefore, this thesis aims to improve forward modelling and inversion performance using novel multi-resolution (MR) grid approach. We implement 3-D forward modelling and data inversion for the DC Resistivity (DCR) and Time Domain Electromagnetic (TDEM) methods on the MR grid. When compared to conventional Staggered (SG) grids, the MR grid implements variable horizontal discretization (resolution) with depth, thus providing simple, but necessary flexibility in grid construction. Fine grid resolution is generally required near the surface to simulate fast variations of EM fields and to depict the shallow complex geometries and measurement configurations. Due to the lossy materials in the subsurface, the variations of the fields become smoother with depth, which is well represented by coarser grid discretization. Furthermore, this can also be viewed as decreasing sensitivity with depth, hence fine grid discretization is also less important for deep regions of the inversion model. The SG grid commonly uses a fine horizontal resolution to ensure accuracy, which is however not needed at depth and results in redundant computations. The MR grid can roughen the discretization with depth and alleviate the over-discretization. As a result, the MR grid can improve the efficiency of forward modelling while maintaining accuracy. Consequently, this improves data inversion performance while preserving the accuracy of inverse models.We realize 3-D DCR forward modelling based on finite-differences discretization, which leads to solving a system of equations for electric potential. Obtained system matrices are hermitian and symmetric in both SG and MR cases. The optimal iterative solution for such systems is based on the Preconditioned Conjugate Gradient (PCG) method, which takes advantage of symmetry and has an optimal convergence rate.The 3-D TDEM forward modelling is implemented using both the explicit scheme based on a modified version of the Du Fort-Frankel method and the implicit scheme based on a second-order backward Euler method. To implement the explicit scheme, we propose a Biot-Savart source term approach to calculate the magnetic field generated by a loop source, which makes the source calculations independent from the grid discretization and thereby improves the flexibility of the modelling setup. In the implicit scheme, the time-stepping is advanced by solving systems of equations. Similarly, the coefficient matrices are converted to be symmetric in both SG and MR grid approaches, and the equations can be efficiently solved using the PCG method as well. Since the initial guess of the solution has a substantial effect on the performance of the iterative solver, we investigate different initial guesses of the solution. Furthermore, we compare the explicit and implicit schemes of TDEM forward modelling in different resistivity scenarios to show their preferable conditions.Based on the algorithm of explicit scheme TDEM forward modelling, we further implement modelling of Geomagnetically Induced Currents (GIC). Line currents are used to simulate the equivalent source in the ionosphere. The 3-D resistivity model of Fennoscandia is modeled with time-varying sources to investigate the inhomogeneous distribution of the induced electric fields.Based on the explicit scheme TDEM forward modelling, we further develop the 3-D TDEM inversion algorithm. The turn-off waveform of the loop transmitter is taken into account in both forward modelling and inversion, and we highlight its importance by illustrating the result of ignoring the turn-off time. The MR grid approach is also used to discretize the inversion model and implement the pseudo modelling for sensitivity computations. We present several synthetic examples to demonstrate the improvement of inversion efficiency using the MR grid compared to the SG grid approach.
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| 29. |
- Gao, Jingyu, et al.
(författare)
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Three-Dimensional Transient Electromagnetic Forward Modeling for Simulating Arbitrary Source Waveform Using Convolution Approach
- 2023
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - : Institute of Electrical and Electronics Engineers Inc.. - 0196-2892 .- 1558-0644. ; 61
-
Tidskriftsartikel (refereegranskat)abstract
- The transient electromagnetic (TEM) method utilizes artificial transmitters and measures electromagnetic (EM) responses to reveal the resistivity information of the subsurface. The current waveform of transmitters has nonnegligible effects on induced fields. Therefore, 3-D TEM forward modeling algorithms need the capability of simulating arbitrary waveforms to obtain accurate responses. In time-stepping-based 3-D TEM forward modeling, the source term (ST) approach is frequently used, which employs the source current density to model the waveform variation during time-stepping. The ST approach, however, requires fine-time discretization to describe complex waveforms, which could significantly raise the computational cost. We present a robust convolution (Conv) approach that computes the convolution between the time derivative of the waveform and the step-off response to incorporate the waveform effects in 3-D TEM modeling. The Conv approach does not discretize the waveform using time steps. Hence, it is advantageous when modeling full-waveform cases. The developed algorithm is based on the finite-element (FE) method using unstructured grids and the implicit backward Euler approach. Both galvanic and inductive transmitters are incorporated. Ground and airborne TEM surveys are tested using an actual airborne TEM waveform, a full waveform of the 2(n) -sequence pseudorandom signal, and various synthetic waveforms. Accuracy is validated against the 1-D and 3-D solutions of published studies. The ST and Conv approaches are compared. Synthetic examples show that the latter approach simplifies the waveform incorporation in TEM modeling and substantially improves time-stepping efficiency without sacrificing accuracy.
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| 30. |
- Guarnieri, Pierpaolo, et al.
(författare)
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Geometry and kinematics of the Triassic rift basin in Jameson Land (East Greenland)
- 2017
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Ingår i: Tectonics. - : American Geophysical Union (AGU). - 0278-7407 .- 1944-9194. ; 36:4, s. 602-614
-
Tidskriftsartikel (refereegranskat)abstract
- The Triassic rift basin along the east Greenland margin described in this paper is represented by NE-SW trending basins and highs segmented by NW-SE trending transfer zones. Coarse-grained sediments along the eastern side of Jameson Land are shown to be hosted in half-graben structures belonging to the Carlsberg Fjord Basin that is bounded by NW dipping normal faults mapped and described after fieldwork in the Klitdal area in Liverpool Land. New aeromagnetic and electromagnetic data together with new drill cores allow the reinterpretation of available seismic lines showing the continuation of the Triassic rift basin toward the SW where it is buried under the Upper Triassic postrift sediments and the Jurassic successions of the Jameson Land Basin. The N-S trending Liverpool Land, interpreted as the boundary block of the Triassic basin, is shown to represent a structural high inherited from the Late Carboniferous tectonics and faulted during the Triassic rifting. The Carlsberg Fjord Basin and the Klitdal Fault System described in this paper should be seen as analogues to the Helgeland Basin in the Norwegian offshore that is bounded by the Ylvingen Fault Zone and to the Papa and West of Shetlands Basins that are bounded by the Spine Fault. The Triassic rift zone and transfer faults on both conjugate margins show a straightforward correlation with the trends of the initial spreading line and fracture zones of the northeast Atlantic indicating a possible inheritance of the Triassic rifting
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- Korja, Toivo, et al.
(författare)
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The geoelectric model of the POLAR Profile, Northern Finland
- 1989
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 162:1-2, s. 113-133
-
Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic soundings have been made in order to construct a geoelectrical (conductivity) model of the crust along the European Geotraverse (EGT) POLAR Profile. Forty magnetotelluric (MT) soundings, eighteen audiomagnetotelluric (AMT) soundings and ten magnetohydrodynamic (MHD) soundings were made on the main POLAR Profile (POLAR I) and ten more MT soundings on a parallel profile (POLAR II), 40 km to the southeast of the main profile. Analysis of simultaneous recordings by the EISCAT magnetometer chain, and thin-sheet modelling of the effect of the Barents Sea, indicate that neither the source field effects nor the presence of the ocean are significant at periods below 200 s in the measurement area. The magnetotelluric data have been modelled with two-dimensional models representing the regional structure along the profiles. In addition to the regional structure, a thin inhomogeneous surface layer is included in the models in order to explain some local features of the measured response functions. Although details of the surface electrical structures are poorly resolved, the gross features of the geoelectrical cross section are considered to be reliable. The results divide the POLAR Profile into three different blocks. The better conducting Karasjok-Kittilä Greenstone Belt in the south has an average resistivity of less than 10 Ωm. The more resistant Lapland Granulite Belt, with a resistivity between 100 and 200 Ωm, is underlain by conductive (< 5 Ωm), N-dipping layers. The depth for the uppermost conductive layer varies from a few kilometres in the southwestern part of the granulite belt to 13 km in the northeastern part, from where it rises steeply towards the surface close to the boundary between the Lapland Granulite Belt and the Inari Terrain. These features appear to be continuous between the two parallel MT profiles. Within the Inari Terrain a conductive zone at an approximate depth of 10 km and with a resistivity of about 20 Ωm was identified in a resistive upper crust. The geoelectric cross section agrees, in gross detail, with the corresponding gravity, refraction seismic and reflection seismic cross sections of the POLAR Profile. All methods indicated a similar shape for the southwestern part of the Lapland Granulite Belt i.e., granulites have a gently NE-dipping boundary against the underlying Karelian Province. In the northeastern part of the granulite belt the geoelectric model and the gravimetric model show a rather steep S-dipping boundary against the Inari Terrain northeast of the granulite belt.
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| 35. |
- Korstgård, John A., et al.
(författare)
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Magnetic anomalies and metamorphic boundaries in the southern Nagssugtoqidian orogen, West Greenland
- 2006
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Ingår i: Geological Survey of Denmark and Greenland Bulletin. - 1811-4598 .- 1604-8156. ; 11, s. 179-184
-
Tidskriftsartikel (refereegranskat)abstract
- Within the southern Nagssugtoqidian orogen in West Greenland metamorphic terrains of both Archaean and Palaeoproterozoic ages occur with metamorphic grade varying from low amphibolite facies to granulite facies. The determination of the relative ages of the different metamorphic terrains is greatly aided by the intrusion of the 2 Ga Kangâmiut dyke swarm along a NNE trend. In Archaean areas dykes cross-cut gneiss structures, and the host gneisses are in amphibolite to granulite facies. Along Itilleq strong shearing in an E-W-oriented zone caused retrogression of surrounding gneisses to low amphibolite facies. Within this Itivdleq shear zone Kangâmiut dykes follow the E-W shear fabrics giving the impression that dykes were reoriented by the shearing. However, the dykes remain largely undeformed and unmetamorphosed, indicating that the shear zone was established prior to dyke emplacement and that the orientation of the dykes here was governed by the shear fabric. Metamorphism and deformation north of Itilleq involve both dykes and host gneisses, and the metamorphic grade is amphibolite facies increasing to granulite facies at the northern boundary of the southern Nagssugtoqidian orogen. Here a zone of strong deformation, the Ikertôq thrust zone, coincides roughly with the amphibolite-granulite facies transition. Total magnetic field intensity anomalies from aeromagnetic data coincide spectacularly with metamorphic boundaries and reflect changes in content of the magnetic minerals at facies transitions. Even the nature of facies transitions is apparent. Static metamorphic boundaries are gradual whereas dynamic boundaries along deformation zones are abrupt.
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| 36. |
- Kumar, Praveen, et al.
(författare)
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An Approach for Fraction of Vegetation Cover Estimation in Forest Above-Ground Biomass Assessment Using Sentinel-2 Images
- 2021
-
Ingår i: Computer Vision and Image Processing. - Singapore : Springer Nature. ; , s. 1-11
-
Konferensbidrag (refereegranskat)abstract
- Forests are one of the most important components to balance and regulate the terrestrial ecosystem on the Earth in protecting the environment. Accurate forest above-ground biomass (AGB) assessment is vital for sustainable forest management to recognize climate change and deforestation for mitigation processes. In this study, Sentinel 2 remote sensing image has been used to calculate the fraction of vegetation cover (FVC) in order to accurately estimate the forest above-ground biomass of Tundi reserved forest in the Dhanbad district located in the Jharkhand state, India. The FVC is calculated in four steps: first, vegetation index image generation; second, vegetation index image rescaled between 0 to 1; third, the ratio of vegetated and non-vegetated areas was calculated with respect to the total image area, and finally, FVC image is generated. In this paper, three vegetation indices have been calculated from the Sentinel 2 image, namely: normalized difference vegetation index (NDVI), normalized difference index 45 (NDI45), and inverted red-edge chlorophyll index (IRECI). Then, the FVC images were generated from the above vegetation indices individually. The ground FVC values were estimated from 22 different locations from the study area. Finally, the image based FVC estimates were compared with the ground estimated FVC. The results show that the IRECI based FVC provided the best approximation to the ground FVC among the different vegetation indices tested.
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| 37. |
- Kumar, Praveen, et al.
(författare)
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Rapid Evaluation and Validation Method of Above Ground Forest Biomass Estimation Using Optical Remote Sensing in Tundi Reserved Forest Area, India
- 2021
-
Ingår i: ISPRS International Journal of Geo-Information. - : MDPI. - 2220-9964. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Optical remote sensing data are freely available on a global scale. However, the satellite image processing and analysis for quick, accurate, and precise forest above ground biomass (AGB) evaluation are still challenging and difficult. This paper is aimed to develop a novel method for precise, accurate, and quick evaluation of the forest AGB from optical remote sensing data. Typically, the ground forest AGB was calculated using an empirical model from ground data for biophysical parameters such as tree density, height, and diameter at breast height (DBH) collected from the field at different elevation strata. The ground fraction of vegetation cover (FVC) in each ground sample location was calculated. Then, the fraction of vegetation cover (FVC) from optical remote sensing imagery was calculated. In the first stage of method implementation, the relation model between the ground FVC and ground forest AGB was developed. In the second stage, the relational model was established between image FVC and ground FVC. Finally, both models were fused to derive the relational model between image FVC and forest AGB. The validation of the developed method was demonstrated utilizing Sentinel-2 imagery as test data and the Tundi reserved forest area located in the Dhanbad district of Jharkhand state in eastern India was used as the test site. The result from the developed model was ground validated and also compared with the result from a previously developed crown projected area (CPA)-based forest AGB estimation approach. The results from the developed approach demonstrated superior capabilities in precision compared to the CPA-based method. The average forest AGB estimation of the test site obtained by this approach revealed 463 tons per hectare, which matches the previous estimate from this test site.
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| 38. |
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| 39. |
- Lyngsie, Stig B., et al.
(författare)
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Regional geological and tectonic structures of the North Sea area from potential field modelling
- 2006
-
Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 413:3-4, s. 147-170
-
Tidskriftsartikel (refereegranskat)abstract
- The spatial distribution of large-scale crustal domains and their boundaries are investigated in the North Sea area by combining gravity, magnetic and seismic data. The North Sea is situated on the plates of three continents, Avalonia, Laurentia and Baltica, which collided during the Caledonian orogeny in the middle Palaeozoic. The location and continuation of the collisional sutures are debated. We apply filters and transformations to potential field data to focus on the crystalline crust and uppermost mantle on a regional scale in order to extract new information on continental sutures. The transformations reveal intrinsic features of crustal transitions between the Caledonian plates and their relation to later extensional structures. The transformations include the Hough Transform applied to the gravity field, calculation of fractional derivatives and integrals of the gravity and magnetic fields, the pseudogravity field and the horizontal gradient field as well as upward continuation. The results indicate a fundamental difference between the lithosphere of Avalonia, Laurentia and Baltica. The location of the Mesozoic rift system (the Central Graben and Viking Graben), may have been partly determined by the presence of the sutures between these three plate, indicative of extensional reactivation of compressional structures. A significant lineament across the entire North Sea between Scotland and North Germany indicates that the lower crust of Baltica provenance may extend as far south-westward as to this lineament. Comparison of the power spectra of the gravity field in five selected areas shows significant differences in the long wavelength components between the areas north and south of the lineament corresponding to differences in crustal properties. This lineament could represent the suture between lithosphere of Caledonian origin (Avalonia) versus lithosphere of Precambrian origin (Baltica) in the lower crust and upper mantle. If this is the case, the lineament is the missing link in the reconstruction of the triple plate collision
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| 40. |
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| 41. |
- Majala, Jonas
(författare)
-
Interpretation of Railway Track Alignment Measurements in a Geodynamic Perspective
- 2021
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development in society means that infrastructure like ballasted railway systems are facing challenges due to request for increased number of high-speed trains and heavier freight trains. This implies that ballasted railways get an increased impact from larger dynamic loads. The question is how the ballasted railways are today affected by dynamic loading and how will an increase in train speed and weight change the soil behaviour within the railway embankment. A method of investigating dynamic soil behaviour is via geophysical measurements. Accelerometers are commonly used for vibration measurements and by installing them on trains are measurements possible to perform for complete railway sections. The knowledge of expected natural frequencies for various track components and soil layers are essential when considering frequency based analysis of vibration measurements. Thus, a frequency based analysis of accelerometer measurements from track recording coaches enables a possible method for analysing the impact of dynamic loads on underlying soil materials with means of a knowledge of expected natural frequencies for various track components and soil layers. Importance to study frequency content of ground motions became more relevant after the Mexico City earthquake 1985 i.e. studies on this specific earthquake revealed amplification of ground motions due to a long duration of shaking and resonance of soil deposits and furthermore causing damage to buildings whose natural period was the same as the period of ground motion. Thus, if we consider a railway with long train sets running along the railway line. Long durations of shaking of the ground can occur as well as a possible resonance of various soil layers leading to changes in material properties. An interesting finding regarding vibration measurements conducted on a track recording coach show that after Fast Fourier Transformation of the measured vibration data, a frequency spectrum analysis indicate possibilities to detect resonance of the ballast layer in the railway embankment. Therefore, this thesis focus on frequency based analysis of the ballast layer were indications of changes in shear modulus of ballast is seen with means of frequency spectrum and theoretical knowledge of the change in shear modulus in ballast material under cyclic loading and increased shear strain. The thesis consists of two main parts, first is the construction of the so-called frequency-based analysis method of track alignment measurements in a geodynamic perspective and the second part is application of the frequency-based method on a case study. Thus, the scientific contribution of this thesis is to increase knowledge of track alignment measurements in the geotechnical field and to provide a frequency based analysis method of track alignment measurements in a geodynamic perspective for evaluation of soil properties. For the actual case study two different railway sections in Sweden is chosen to enable a comparison, especially when these sections differ with respect to one having only a ballast layer and subgrade and one having ballast, sub ballast and subgrade. Thus, the section with only ballast and subgrade enable a clearer analysis since these layers have large difference in natural frequency. First section is located at Tolikberget in the north part of Sweden and second one between Stenkumla and Dunsjö in south of Sweden. From the analysis of the selected sections it is possible to see indications from the frequency spectrum that the vibration measurements capture the natural frequencies of ballast material associated to the maximum shear modulus and to varying degrees of reduced shear modulus due to increased shear strain. Thus, it can be concluded that vibration measurements conducted on track recording coaches have potential to be used for studies of changes in ballast materials dynamic properties.
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| 42. |
- Matzka, Jürgen, et al.
(författare)
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A new aeromagnetic survey of the North Pole and the Arctic Ocean north of Greenland and Ellesmere Island
- 2010
-
Ingår i: Earth Planets and Space. - : Society of Geomagnetism and Earth, Planetary and Space Sciences. - 1343-8832 .- 1880-5981. ; 62:10, s. 829-832
-
Tidskriftsartikel (refereegranskat)abstract
- We present a preliminary analysis of more than 50,000 km of aeromagnetic survey lines flown in the Arctic Ocean, acquired in 2009 with an optically pumped scalar magnetometer as part of the airborne geophysical survey 'LOMGRAV'. From the observations we removed main and magnetospheric fields as given by the CHAOS-3 field model (Olsen et al., 2010) and remaining external fields as monitored by the Canadian magnetic observatory Alert. The reduced data were levelled based on cross-over differences at line intersections. Finally, a grid was computed, upward continued by 3500 m and compared with the EMAG2 grid (Maus et al., 2009), showing a good general agreement but also areas with systematic differences. The obtained data are expected to be part of the next version of the World Digital Magnetic Anomaly Map (WDMAM).
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| 43. |
- Pedersen, Laust Börsting, et al.
(författare)
-
Construction of component maps from aeromagnetic total field anomaly maps
- 1990
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Ingår i: Geophysical Prospecting. - : Wiley-Blackwell. - 0016-8025 .- 1365-2478. ; 38:7, s. 795-804
-
Tidskriftsartikel (refereegranskat)abstract
- Total field anomalies as defined from normal aeromagnetic surveys give good approximations of the anomalous components along the direction of the main geomagnetic field, which is generally much larger than the anomalous field. Using the relations between vertical and horizontal components of the field, the total field anomaly is related to any vertical or horizontal component and the corresponding horizontal and vertical derivatives. An example from the Siljan impact structure indicates that such directional filters may be applied to extract useful information from magnetic maps.
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| 44. |
- Pedersen, Laust Börsting, et al.
(författare)
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Electric resistivity in the Gravberg-1 deep well, Sweden
- 1992
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 97:6B, s. 9171-9182
-
Tidskriftsartikel (refereegranskat)abstract
- The Siljan impact structure located in central Sweden has been the object of intense geophysical and geological studies for several decades. This paper presents the results of electrical resistivity measurements on the surface, in the hole, and on core samples from shallow coreholes distributed over the whole impact structure. Magnetotelluric data constrain the central part of the structure to be essentially one-dimensional with an upper crustal unit of about 10 000 Ωm followed by a less resistive impact related unit of 1000 Ωm from a depth of about 6 km to a depth of 20 km. The lower crust is a homogeneous unit of about 300 Ωm extending down to about 40 km, where the upper mantle is marked by an increase in resistivity of about 1000 Ωm. Major fracture zones, some of which coincide with the horizontal dolerite sills, known to extend over tens of kilometers, are probably the main carriers of current. Saline fluids recovered below 5.4-km depth and the magnetotelluric results lead us to conclude that pore fluids are highly saline below this depth even on a regional scale.
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| 45. |
- Pedersen, Laust Börsting, et al.
(författare)
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Inversion Of Magnetotelluric Data: A Non‐Linear Least‐Squares Approach
- 1989
-
Ingår i: Geophysical Prospecting. - : Wiley-Blackwell. - 0016-8025 .- 1365-2478. ; 37:6, s. 669-695
-
Tidskriftsartikel (refereegranskat)abstract
- The inverse problem of magnetotellurics over a horizontally stratified earth is described, with emphasis on practical application. The inversion is divided into basically two steps. The construction of some best solution, and the analysis of that solution with regard to uncertainty and complexity. For the construction of best solutions a robust non‐linear solver was developed, and for the estimation of parameter errors a modified eigenvalue‐eigenvector analysis is performed to better describe non‐linear effects. The choice of the number of layers is shown to be intimately connected with the structure of data errors and the misfit between model and data. An example from the Siljan impact structure in Sweden illustrates the power of the technique.
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| 46. |
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| 47. |
- Pedersen, Laust Börsting, et al.
(författare)
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The gradient tensor of potential field anomalies: some implications on data collection and data processing of maps
- 1990
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Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 55:12, s. 1558-1566
-
Tidskriftsartikel (refereegranskat)abstract
- The full gradient tensor is presently not measured routinely onboard airplanes or on land. This paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available. We suggest that, in addition to producing for example standard total field anomaly maps, the invariants of the tensor be mapped
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| 48. |
- Pilbeam, L. H., et al.
(författare)
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Inverse Modeling to Constrain Composition of CO2-Rich Parental Melt of Kimberlite: Model Development and Application to the Majuagaa Dyke, Southern West Greenland
- 2023
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Ingår i: Journal of Petrology. - : Oxford University Press. - 0022-3530 .- 1460-2415. ; 64:2
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Tidskriftsartikel (refereegranskat)abstract
- A model is developed to test the hypothesis that kimberlites can form by low-degree melting of asthenospheric mantle followed by entrainment and assimilation of lithospheric mantle. The developed model uses inversion calculations based upon rare earth and compatible trace elements. For kimberlites (s.s.), an equation describing mass balance between a melt of unknown composition and a contaminant end-member of xenocrystic/assimilated material from the lithospheric mantle is inverted. This allows calculation of the mass fraction of xenocrystic minerals from the lithospheric mantle (olivine, orthopyroxene, clinopyroxene, garnet, ilmenite) entrained in the kimberlitic magma, as well as the source mineralogy and melt degree in the source region.The composition of the parental melt prior to interaction with the lithosphere is not assumed a priori but is calculated by the model. The CO2, H2O, K2O and P2O5 contents of the source are estimated assuming batch melting and the inversion models. The range and coupling of the model parameters are found using a non-linear most-squares inversion procedure, and the model space is visualised using a Self-Organising Map approach. Our earlier work supporting assimilation of xenocrystic opx is, however, not a precondition but provides a post-processing constraint, as well as the selection of a more likely set of solutions from the Self-Organising Map.The calculation is applied to a data set from the Majuagaa kimberlite dyke (southern West Greenland) including added whole rock analyses for CO2 and H2O. Major variations in whole rock compositions are related to flow differentiation of olivine macrocrysts. The textures of opx, cpx, gt and ilm megacrysts show evidence for reaction with the transporting melt and physical erosion in the kimberlitic mush. Using the bulk rocks in our inversion scheme results in a silico-carbonatite parental melt with major element concentrations consistent with experimental melts. The ol, opx, and cpx mass fractions in the source are not well-resolved by this calculation, but the proportion of gt in the source is comparatively well defined at 15–22 wt% and cpx is constrained to less than 14 wt%. The source assemblage required is 36–80 wt% ol, 2–49 wt% opx, 0–6 wt% cpx, and 15–19 wt% gt. This suggests a peridotitic rather than an eclogitic source.The inversion model gives an overall mass fraction of xenocrystic material in the Majuagaa kimberlite magma of 41–51 wt% The mass fractions of the xenocryst phases are as follows: 71–85 wt% ol, 0–13 wt% opx, 5 ± 1 wt% gt, and 10–14 wt% ilm. There is less than 3 wt% cpx in the xenocrystic and assimilated assemblage. These results agree with petrographic observations. Processing the model results using the Self-Organising Map clearly displays the extent and coupling within the statistically acceptable region of the model space and leads us to a preferred model of 49 wt% xenocrysts with a xenocryst assemblage of 71–76 wt% ol, 8–13 wt% opx, 4 wt% gt and 12 wt% ilm.A source with a REE pattern similar to that of primitive mantle is sufficient to form the parental melt and consistent with generation of the initial kimberlite melt in the convecting mantle. Calculated CO2 and H2O concentrations in the source of the Majuagaa kimberlite of 230–860 μg/g and 223–741 μg/g, respectively, are within the range of independent convecting mantle estimates. This is equivalent to <0.17 wt% magnesite and the H2O budget of the mantle source can be accommodated via storage in nominally anhydrous silicate phases.When applied to Majuagaa kimberlite, the inversions are consistent with a conceptually simple model of kimberlite formation: (1) low degree melting in carbonated asthenospheric peridotite, (2) melt extraction and concentration, and (3) entrainment and reaction with lithospheric mantle material.
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- Planke, Sverre, et al.
(författare)
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Seismic characteristics and distribution of volcanic intrusions and hydrothermal vent complexes in the Vøring and Møre basins
- 2005
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Ingår i: Petroleum Geology Conference Proceedings. - : Petroleum Geology Conferences. - 2047-9921. ; 6, s. 833-844
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Tidskriftsartikel (refereegranskat)abstract
- A voluminous magmatic complex was emplaced in the Vøring and Møre basins during Paleocene/ Eocene continental rifting and break-up in the NE Atlantic. This intrusive event has had a significant impact on deformation, source-rock maturation and fluid flow in the basins. Intrusive complexes and associated hydrothermal vent complexes have been mapped on a regional 2D seismic dataset (c.150 000 km) and on one large 3D survey. The extent of the sill complex is at least 80 000 km2, with an estimated total volume of 0.9 to 2.8 × 104 km3. The sheet intrusions are saucer-shaped in undeformed basin segments. The widths of the saucers become larger with increasing emplacement depth. More varied intrusion geometries are found in structured basin segments. Some 734 hydrothermal vent complexes have been identified, although it is estimated that 2-3000 vent complexes are present in the basins. The vent complexes are located above sills and were formed as a direct consequence of the intrusive event by explosive eruption of gases, liquids and sediments, forming up to 11 km wide craters at the seafloor. The largest vent complexes are found in basin segments with deep sills (3-9km palaeodepth). Mounds and seismic seep anomalies located above the hydrothermal vent complexes suggest that the vent complexes have been re-used for vertical fluid migration long after their formation. The intrusive event mainly took place just prior to, or during, the initial phase of massive break-up volcanism (55.0-55.8Ma). There is also evidence for a minor Upper Paleocene volcanic event documented by the presence of 20 vent complexes terminating in the Upper Paleocene sequence and the local presence of extrusive volcanic rocks within the Paleocene sequence
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